S. epidermidis agr system regulates biofilm formation and initial cell attachment through atlE . ( a-d) S. epidermidis 1457 wild type (wt, a and d), agr mutant (△ agr, b and e) and agr/atlE double mutant (△ agr/atlE, c and f) were grown for 24 h in flow chambers irrigated with minimal medium, and were then stained with SYTO 9 and PI, upon which microscopic investigation was performed by CLSM. The 3-D images (d-f) were generated using the IMARIS, bars, 50 μm. (g) Biofilm biomass in microtitre plates was quantified using a crystal violet assay. (h) Initial attachment of S. epidermidis strains in static chambers was quantified as described in Methods. Error bars represent the S.E.M. for three independent experiments.